The present disclosure relates to an electrographic image forming apparatus.
An electrographic image forming apparatus applying an intermediate transfer type in order to form a color image is widely known. The intermediate transfer type image forming apparatus includes a plurality of photosensitive bodies, an intermediate transferring belt, a first transferring part, a second transferring part and a cleaning device. The photosensitive bodies carry toner images of a plurality of colors. The intermediate transferring belt as an image carrier comes into contact with the photosensitive bodies. The first transferring part transfers the toner image on each photosensitive body to a surface of the intermediate transferring belt. The second transferring part transfers the color toner images on the intermediate transferring belt onto a sheet in a lump. The cleaning device removes a toner not transferred onto the sheet (hereinafter, called as a “remained toner”) from the surface of the intermediate transferring belt.
As the cleaning device of the intermediate transfer type image forming apparatus, a bias cleaning manner is widely applied. The bias cleaning manner is a manner removing the remained toner from the surface of the intermediate transferring belt by a cleaning member to which a bias of a reversed polarity to a charged polarity of the remained toner is applied. The intermediate transferring belt has a plurality of layers including an elastic layer for the purpose of lifetime extension and image quality enhancement of an output image.
The intermediate transfer type image forming apparatus has excellent productivity because of transferring the color toner images onto the surface of the intermediate transferring belt in a lump, but tends to increase an amount of the remained toner on the intermediate transferring belt because of overlapping the toner images of respective colors on the surface of the intermediate transferring belt. In a case of overlapping the toners to form the color image, because the charging amount of the overlapped toners is increased, voltage required for transferring is also increased. Due to deterioration of a developer, a polarity of the remained toner may become reversed from that in developing process or become close to no polarity. If these factors are simultaneously or repeatedly caused, there is a possibility that the cleaning device including the above-mentioned cleaning member cannot efficiently remove the remained toner from the surface of the intermediate transferring belt.
Thereupon, a cleaning device efficiently removing the remained toner from the surface of the intermediate transferring belt is proposed. For example, there is the cleaning device which includes a cleaning member coming into contact with the intermediate transferring belt and an auxiliary cleaning member coming into contact with the intermediate transferring belt at an upstream side from the cleaning member. The auxiliary cleaning member frictionally charges the remained toner to a predetermined polarity (a polarity in the developing process). Because of this, the cleaning member easily removes the remained toner from the surface of the intermediate transferring belt by the bias cleaning manner.
Recently, from a viewpoint of reduction of cost and reuse of resources, low quality sheet, such as a recycled paper, may be used. In a region manufacturing the sheet by manufacturing equipment with insufficient performance, it may be necessary to use the low quality sheet.
Such a low quality sheet may contain a large quantity of talc or calcium carbonate as a surface preparation agent or a filler. If image forming operation is repeatedly carried out to such a sheet, paper dust containing the talc or the calcium carbonate is adhered onto a surface of an image carrier. Particularly, if the above-mentioned low quality sheet is used at a stage before whitening of the surface of the image carrier (a phenomenon in which the surface of the image carrier is whitened mainly because external additive is accumulated onto the surface of the image carrier) reaches a predetermined level, a large quantity of the paper dusts containing the talc or the calcium carbonate are adhered onto the surface of the image carrier. If the paper dust on the surface of the image carrier is frictionally charged by the auxiliary cleaning member, the cleaning member and auxiliary cleaning member are clogged with the paper dust. Because of this, functionality of the auxiliary cleaning member frictionally charging the remained toner is deteriorated.
Because the cleaning member is contracted as the use is continued, functionality of the cleaning member mechanically scraping the remained toner is deteriorated. The functionality deterioration of the cleaning member hinders image forming from being carried out excellently on a long time. The paper dust with which the auxiliary cleaning member is clogged may be hardened to scrape a surface layer of the image carrier. In such a case, there is a trouble that a friction coefficient at a scraped portion is increased and second transfer performance of the image carrier is deteriorated.